We propose an integrated program of basic and translational research to develop foamy virus (FV) vector- based gene replacement therapy for patients who suffer from the inherited severe combined immunodeficiency SCID-X1. The program involves three scientific Projects and four Cores. Two of the scientific projects are focused on studying FV vector SCID-X1 gene therapy using animal models: Project 1 - Pre-clinical modeling of FV gene therapy for murine and human SCID-X1, and Project 2 - FV mediated gene therapy in the canine SCID-X1 model. These projects will test key hypotheses regarding the safety and efficacy of FV vectors applied in conjunction with advanced non-myeloablative conditioning regimens for ?c gene replacement therapy. The other scientific project, Project 3 - Second generation approaches to FV vector SCID-X1 gene therapy, will test key hypotheses related to FV vector systems and technology, with the goal of further enhancing FV vector safety and performance. The three Projects will be supported by four Cores to provide for efficient use of common methods and technology. Over the five year period of support, the program is designed to yield an integrated gene replacement therapy for SC1D-X1 consisting of a well characterized 1st generation clinical ?c FV vector and an advanced conditioning regimen that is fully ready for translation to a human SCID-X1 clinical trial. In addition, the program wil advance our knowledge of FV vector systems and FV vector technology; and initiate pre-clinical evaluation of 2nd generation ?c FV vector systems and integrated therapies anticipated to lead to future further advances in safety and efficacy. Overall, our work is predicted to lead to safe and novel future therapies, including efficient methods for direct in vivo FV vector gene delivery, needed for human SCID-X1 as well other genetic disorders. RELEVANCE: This project will create a new type of gene therapy for patients who suffer from the catastrophic immunodeficiency SC1D-X1. It will also generate advances in gene therapy and stem cell transplantation that have the potential to lead to safer and more effective therapies for many other types of inherited diseases of the blood and immune system. PROJECT 1 - Pre-clinical Modeling of Foamy Viral Gene Therapy Project Leader (PL): David J. Rawlings (Description as provided by applicant): SCID-X1 is catastrophic immunodeficiency disorder caused by mutations within the common gamma chain (?c) gene. While stem cell transplantation using a matched sibling donor can be curative, most patients lack optimal donors leading to poorer outcomes. Gene replacement has many theoretical advantages as an alternative therapeutic approach for SCID-X1; and pioneering clinical studies using gammaretroviral ?c delivery lead to both significant benefit as well as unanticipated adverse events due to viral enhancer triggered leukemogenesis. The overarching hypothesis of this PPG is that both the efficacy and safety of ?c gene delivery can be significantly improved using recombinant foamy virus (FV) based vectors. Studies in Project 1 are designed to test the hypotheses that ?c FV vectors devoid of viral enhancers (with or without additional enhancer blocking elements flanking the transcriptional cassette) will exhibit levels of transgene expression sufficient for functional rescue in vivo while concurrently showing reduced genotoxicity. The aims of Project 1 are designed to test these hypotheses via detailed phenotypic, functional, and molecular analysis in both: 1) a small animal model of SCID-X1 and 2) hematopoietic stem cells (HSC) derived from SCID-X1 patients. Our specific studies will include efficacy and safety assessment of 1) EF1?-hu-?c FV vectors in vivo in myeloablated vs. non-myeloablated murine SCID-X1 recipients; and in alternative in vitro transactivation assays; 2) Preclinical and GMP-grade 1st generation ?c FV in transduced SCID-X1 patient CD34+ BM cells; and 3) Candidate insulated 2nd generation ?c FV vectors in HSC from SCID-X1 mice and human patients. Project 1 will utilize all 4 Cores and will interface on multiple levels with work within both Projects 2 and 3. In conjunction with data derived from Projects 2 and 3, our studies will provide key data regarding efficacy, safety and optimal vector design for future 1st and 2nd generation SCID-X1 FV vector clinical trials. RELEVANCE: SCID-X1 is severe immune disorder caused by mutations in the ?c gene. Gene therapy is predicted to provide a beneficial treatment for SCID-X1. However, previous approaches, while beneficial, also lead to a high frequency of adverse events. The goal of this PPG is develop safe and effective SCID-X1 gene delivery using recombinant foamy virus (FV) based vectors. Studies in Project 1 are designed to test the idea that candidate clinical SCID-X1 FV vectors will rescue function in mouse and human models of SCID-X1 while concurrently showing reduced genotoxicity.